The present invention relates to a method of flowing pressurized fluid into one or more internal passages of a casting to remove ceramic cote or other material.
In the investment casting of nickel or cobalt based superalloy turbine airfoils (e.g. turbine blades and vanes), a ceramic core is positioned in the investment shell mold to produce cooling air passages internal of the casting when the molten superalloy is cast and solidified in the mold about the core.
Following casting, the ceramic core must be removed from the casting to leave the internal air cooling passages therein. In the past, the ceramic core has been removed from the cast turbine airfoil by an autoclave technique, open kettle technique or other technique. One autoclave technique involves immersing the casting in an aqueous caustic solution (e.g. 45% KOH) at elevated pressure and elevated temperature (e.g. 250 psi and 177 degrees C) for an appropriate time to dissolve or leach the core from the casting. U.S. Pat. Nos. 4,134,777 and 4,141,781 disclose autoclave techniques to remove a ceramic core.
An exemplary open kettle technique involves immersing the casting in a similar aqueous caustic solution at ambient pressure and elevated temperature (e.g. 132 degrees C) with agitation of the solution for a time to dissolve or leach the core from the casting.
U.S. Pat. No. 5,915,452 discloses removing a ceramic core from a casting using a caustic fluid at elevated temperature sprayed under pressure at an exposed region of the core in the casting.
U.S. Pat. No. 5,778,963 describes core removal using a caustic solution sprayed at a pressure of 5000 to 10,000 psi at the core in the casting. The patent indicates that ceramic core residue can be removed by directing a stream of water or steam at the casting following the high pressure spraying treatment.
U.S. Pat. No. 4,439,241 describes a caustic autoclave treatment to soften engine run deposits in internal airfoil passages followed by a waterblast treatment where water is sprayed at greater than 2000 psi from a spray nozzle through the passages to remove any remaining softened deposits from the internal passages.
An object of the present invention is to provide an improved method for removing material from an internal passage of a metallic body such as, for example, internal passages of a casting.
The present invention provides in one embodiment a method of flowing a fluid into an internal passage of a body, such as a metallic casting, to remove ceramic core material or other material therefrom under CNC control of a fluid spray nozzle in a manner that the fluid spray nozzle is caused to laterally scan a two dimensional area of each opening of one or more passages at an exterior casting surface to improve removal of ceramic core or other material residing in the passage. In an illustrative embodiment of the invention, an area of each opening of an internal passage at an exterior casting surface is scanned laterally in X and Y orthogonal directions with a fluid spray nozzle under CNC control. Motion of the fluid spray nozzle in a Z axis orthogonal to the X and Y axes also is CNC controlled to provide optimum positioning of the spray nozzle relative to the passage opening.
The present invention provides in another embodiment a method of flowing a fluid into an internal passage of a casting to remove ceramic core material or other material therefrom under CNC control of a fluid spray nozzle in a manner that the fluid spray nozzle is caused to orbitally scan a two dimensional area of each opening of one or more passages at an exterior casting surface.
Openings at the root end, tip end or trailing edge of a gas turbine engine airfoil superalloy casting (e.g. turbine blade or vane) can be scanned under CNC control pursuant to embodiments of the invention to remove residual ceramic core material from internal cooling passages.
The objects and advantages of the present invention will become more readily apparent from the following description taken with the following drawings.